A RAN is a network between mobile devices and a core network. In the RAN, wireless base stations located at remote cell sites perform digital baseband processing. However, in a C-RAN, RRUs replace the wireless base stations and centralized BBUs located at central sites near the core network perform the digital baseband processing. The RRUs interface with antennas for wireless RF transmission and reception. The RRUs require limited digital baseband processing.
In the C-RAN, a fronthaul connects the BBUs to the RRUs. CPRI, a standard for fronthauls, describes digitizing wireless channels to create digitized channels, aggregating the digitized channels to create aggregated channels, and communicating the aggregated channels using aggregated fiber optical channels or aggregated microwave channels. The aggregated channels have high data rates that necessitate complex communications systems.